Display device

ABSTRACT

According to one embodiment, a display device includes an insulating substrate, a thin-film transistor including a semiconductor layer formed on a layer above the insulating substrate, a gate electrode which at least partly overlaps the semiconductor layer, and a first electrode and a second electrode which are electrically connected to the semiconductor layer, and a light shielding layer formed between the thin-film transistor and the insulating substrate to at least partly overlap the semiconductor layer, the light shielding layer electrically connected to the gate electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. application Ser. No. 15/662,385 filedJul. 28, 2017, which is a continuation of U.S. application Ser. No.15/444,379 filed Feb. 28, 2017 (now U.S. Pat. No. 9,772,536 issued Sep.26, 2017), which is a continuation of U.S. application Ser. No.14/990,201 filed Jan. 7, 2016 (now U.S. Pat. No. 9,618,813 issued Apr.11, 2017), and claims the benefit of priority under 35 U.S.C. § 119 fromJapanese Patent Application No. 2015-005828 filed Jan. 15, 2015, theentire contents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

In active matrix display devices, a thin-film transistor (TFT) is usedas a switching element of a pixel. A thin-film transistor is also usedas a switching element of a driver formed in a frame area (non-displayarea) outside an active area (display area).

The thin-film transistor includes a semiconductor layer. When light isincident on the semiconductor layer, light leakage current is produced.The light leakage current may decrease the contrast, and the performanceof the display device may be deteriorated. To suppress such performancedeterioration of the display device by the light leakage current, thereis a well-known technique of forming a light shielding layer on an arraysubstrate.

Furthermore, a light shielding layer in a floating state causes a backgate effect on a thin-film transistor. To suppress the back gate effect,there is a well-known technique of electrically connecting the lightshielding layer to other components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view which shows the structure of a display device andan equivalent circuit of an embodiment.

FIG. 2 is a plan view which shows an array substrate of FIG. 1 in apartly enlarged manner.

FIG. 3 is a cross-sectional view which shows the array substrate takenalong line of FIG. 2.

FIG. 4 is a cross-sectional view which shows the array substrate takenalong line IV-IV of FIG. 2.

FIGS. 5A and 5B are cross-sectional views which shows a manufacturingmethod of a thin-film transistor of FIGS. 3 and 4.

FIGS. 6A and 6B are cross-sectional views which shows the manufacturingmethod of the thin-film transistor of FIGS. 3 and 4, subsequently toFIG. 5.

FIGS. 7A and 7B are cross-sectional views which shows the manufacturingmethod of the thin-film transistor of FIGS. 3 and 4, subsequently toFIG. 6.

FIGS. 8A and 8B are cross-sectional views which shows the manufacturingmethod of the thin-film transistor of FIGS. 3 and 4, subsequently toFIG. 7.

FIGS. 9A and 9B are cross-sectional views which shows the manufacturingmethod of the thin-film transistor of FIGS. 3 and 4, subsequently toFIG. 8.

FIGS. 10A and 10B are cross-sectional views which shows themanufacturing method of the thin-film transistor of FIGS. 3 and 4,subsequently to FIG. 9.

FIGS. 11A, 11B and 11C include plan views and cross-sectional views of athin-film transistor of a display device of a first variation.

FIG. 12 is a schematic cross-sectional view which shows a display deviceof a second variation.

FIG. 13 is a cross-sectional view which shows an array substrate takenalong line XIII-XIII of FIG. 12.

FIG. 14 is a cross-sectional view which shows the array substrate takenalong line XIV-XIV of FIG. 12.

FIGS. 15A and 15B are cross-sectional views which shows a manufacturingmethod of a thin-film transistor of FIGS. 13 and 14.

FIGS. 16A and 16B are cross-sectional views which shows themanufacturing method of the thin-film transistor of FIGS. 13 and 14,subsequently to FIG. 15.

FIGS. 17A and 17B are cross-sectional views which shows themanufacturing method of the thin-film transistor of FIGS. 13 and 14,subsequently to FIG. 16.

FIGS. 18A and 18B are cross-sectional views which shows themanufacturing method of the thin-film transistor of FIGS. 13 and 14,subsequently to FIG. 17.

FIGS. 19A and 19B are cross-sectional views which shows themanufacturing method of the thin-film transistor of FIGS. 13 and 14,subsequently to FIG. 18.

FIGS. 20A, 20B and 20C include plan views and cross-sectional views of athin-film transistor of a display device of a third variation.

DETAILED DESCRIPTION

In general, according to one embodiment, a display device includes aninsulating substrate, a thin-film transistor including a semiconductorlayer formed on a layer above the insulating substrate, a gate electrodewhich at least partly overlaps the semiconductor layer, and a firstelectrode and a second electrode which are electrically connected to thesemiconductor layer, and a light shielding layer formed between thethin-film transistor and the insulating substrate to at least partlyoverlap the semiconductor layer, the light shielding layer electricallyconnected to the gate electrode.

Embodiments will be described hereinafter with reference to theaccompanying drawings. Incidentally, the disclosure is merely anexample, and proper changes within the spirit of the invention, whichare easily conceivable by a skilled person, are included in the scope ofthe invention as a matter of course. In addition, in some cases, inorder to make the description clearer, the widths, thicknesses, shapes,etc. of the respective parts are schematically illustrated in thedrawings, compared to the actual modes. However, the schematicillustration is merely an example, and adds no restrictions to theinterpretation of the invention. Besides, in the specification anddrawings, the structural elements having functions, which are identicalor similar to the functions of the structural elements described inconnection with preceding drawings, are denoted by like referencenumerals, and an overlapping detailed description is omitted unlessotherwise necessary.

FIG. 1 is a plan view which shows the structure of a display device 1and an equivalent circuit of the present embodiment. In the followingdescription, a liquid crystal display device is given as an example ofthe display device with a thin-film transistor.

As shown in FIG. 1, the display device 1 includes an active are (displayarea) ACT used for image display and a frame area (non-display area)outside the active area ACT. The display device 1 includes a liquidcrystal display panel PLN. The liquid crystal display panel PLN includesan array substrate AR, countersubstrate (described later), and liquidcrystal layer. In the active area ACT, the array substrate AR includes ngate lines G (G1 to Gn), n auxiliary capacitance lines C (C1 to Cn), msource lines S (S1 to Sm), and pixels PX in an m×n matrix. Each pixel PXis defined by two adjacent gate lines G and two adjacent source lines S.

Gate lines G and auxiliary capacitance lines C extend substantiallyparallel to each other in a first direction X. Note that the gate linesG and auxiliary capacitance lines C do not necessarily extend linearly.The gate lines G and auxiliary capacitance lines C are arranged in asecond direction Y alternately. Source lines S extend substantiallyparallel to each other in the second direction Y. The source lines S aresubstantially orthogonal to the gate lines G and auxiliary capacitancelines C. Note that the source lines S do not necessarily extend parallelto each other. Note that the gate lines G, auxiliary capacitance linesC, and source lines S may be formed to partly bend. The gate lines G,source lines S, and auxiliary capacitance lines C may be formed ofmolybdenum, chrome, tungsten, aluminum, copper, titanium, nickel,tantalum, and silver, or may be formed of an alloy of such elements;however, no limitation is intended thereby. They may be formed of othermetals, alloys, or a layered film of such metals and alloys.

Each gate line G extends outside the active area ACT and is connected toa gate driver GD. Each source line S extends outside the active area ACTand is connected to a source driver SD. Each auxiliary capacitance lineC extends outside the active area ACT and is electrically connected to avoltage applier VCS to which an auxiliary capacitance voltage isapplied.

Each pixel PX includes a thin-film transistor TR1, pixel electrode PE,common electrode CE, and retention capacitance CS. The pixel electrodePE is electrically connected to a source line S via thin-film transistorTR1. The common electrode PE is opposed to the pixel electrode PE withthe liquid crystal layer interposed therebetween. The common electrodeCE is electrically connected to a power supplier VCOM disposed outsidethe active area ACT. The retention capacitance CS is electricallyconnected to the pixel electrode PE.

Thin-film transistor TR1 is switched between conductive (on) andnonconductive (off) by control signals supplied from the gate driver GDthrough the gate line G. Image signals output from the source driver SDare supplied to the pixel electrode PE through the source line S andconductive thin-film transistor TR1. The voltage applied to the liquidcrystal layer is controlled by a potential difference between the commonelectrode CE which is set to the common voltage and the pixel electrodePE.

Note that, although the structure of the display panel PNL is notdetailed here, display modes used therein include the followingexamples. In a display device which mainly uses a vertical field displaymode such as twisted nematic (TN) mode, optically compensated bend (OCB)mode, and vertically aligned (VA) mode, the pixel electrode PE isprovided with the array substrate AR while the common electrode CE isprovided with the countersubstrate CT. In a display device which mainlyuses a transverse field display mode such as in-plane switching (IPS)mode and fringe field switching (FFS) mode, both the pixel electrode PEand the common electrode CE are provided with the array substrate AR.

The retention capacitance CS retains the voltage applied to the liquidcrystal layer for a certain period of time, and is composed of a pair ofelectrodes opposed to each other with an insulating layer interposedtherebetween. For example, in the retention capacitance CS, oneelectrode is part of the auxiliary capacitance line or an auxiliaryelectrode which is electrically connected to the auxiliary capacitanceline CS, and the other electrode is an auxiliary counterelectrode whichis connected to the pixel electrode PE.

The gate driver GD and the source driver SD are formed in the framearea. Each of the gate driver GD and the source driver SD includes aplurality of thin-film transistors TR2 which function as switchingelements.

FIG. 2 is a plan view which shows the array substrate AR in a partlyenlarged manner. Note that, in the figure, only the main parts which arenecessary for the explanation are depicted out of the entire structureof the array substrate AR. Thin-film transistor TR1 of the structure ofFIG. 2 is of a top-gate type.

As shown in FIG. 2, the array substrate AR includes the source line S,gate line G, pixel electrode PE, semiconductor layer SC, light shieldinglayer LS, connection electrode EL, and the like.

The gate line G extends in the first direction X. The source line Sextends in the second direction Y to cross the gate line G.

Thin-film transistor TR1 is disposed in the proximity of a crossingpoint of the gate line G and the source line S, and is electricallyconnected to the gate line G and the source line S. Thin-film transistorTR1 includes the semiconductor layer SC, gate electrode WG which isformed integrally with the gate line G, source electrode (firstelectrode) 15A which is formed integrally with the source line S, anddrain electrode (second electrode) 15B. The semiconductor layer SC isformed in a rectangular shape having its long sides along the firstdirection X and short sides along the second direction Y. The sourceelectrode 15A is electrically connected to the semiconductor layer SCthrough a contact hole (second contact hole) CH2. The drain electrode15B is formed in an island shape, and is electrically connected to thesemiconductor layer SC through a contact hole (third contact hole) CH3.The gate electrode WG projects from the gate line G in the seconddirection Y and is disposed on the upper layer of the semiconductorlayer SC.

In the example depicted, the pixel electrode PE is formed in asubstantial rectangular shape having its long sides in the firstdirection X and short sides in the second direction Y. The pixelelectrode PE contacts the drain electrode 15B of thin-film transistorTR1 through a contact hole which is not shown.

The light shielding layer LS overlaps the semiconductor layer SC and thegate electrode WG. A projection LSa is formed on the light shieldinglayer LS to project from the area overlapping the gate electrode WG.Projection LSa extends in a direction (second direction Y) which isorthogonal to the longitudinal direction (first direction X) of thesemiconductor layer SC, and extends in a direction opposite to the pixelelectrode PE from the light shielding layer LS. In the presentembodiment, projection LSa extends in the area overlapping the gate lineG.

The connection electrode EL is formed in an island shape and iselectrically connected to the gate electrode WG and the light shieldinglayer LS through a contact hole (first contact hole) CH1 formed onprojection LSa. That is, the gate electrode WG and the light shieldinglayer LS are electrically connected to each other by the connectionelectrode EL. The connection electrode EL contacts, as described later,a side surface and the upper surface of projection LSa.

FIG. 3 is a cross-sectional view which shows the array substrate ARtaken along line of FIG. 2.

As shown in FIG. 3, the array substrate AR further includes aninsulating substrate 10, first insulating film 11, and fourth insulatingfilm 14, and the like.

The insulating substrate 10 is formed of a light-transmissive andinsulative material such as glass, resin, or the like. Here, the uppersurface 10A of the insulating substrate 10 is a surface parallel to theX-Y plane which is defined by the first direction X and the seconddirection Y orthogonal to each other. A third direction Z is the normalto the main surface of the insulating substrate 10 and is vertical toboth the first direction X and the second direction Y.

The light shielding layer LS is formed in the upper surface 10A of theinsulating substrate 10. The light shielding layer LS is covered withthe first insulating film 11. Thin-film transistor TR1 is formed abovethe light shielding layer LS to function as a switching element.Thin-film transistor TR1 includes the semiconductor layer SC, secondinsulating film 12, gate electrode WG, third insulating film 13, sourceelectrode (first electrode) 15A, and drain electrode (second electrode)15B.

The semiconductor layer SC is formed on a layer above the insulatingsubstrate 10, and in the present embodiment, is formed on the firstinsulating film 11. The semiconductor layer SC includes a source regionSCS, drain region SCD, and channel region SCC. The channel region SCC isdisposed between the source region SCS and the drain region SCD. Thesource region SCS and the drain region SCD are formed to have lowerresistance as compared to the channel region SCC. The light shieldinglayer LS is formed between thin-film transistor TR1 and the insulatingsubstrate 10, and is opposed to at least the channel region SCC of thesemiconductor layer SC.

In the present embodiment, the semiconductor layer SC is formed of anoxide semiconductor. Such an oxide semiconductor may preferably be anoxide containing at least one of indium, gallium, and zinc. As typicalexamples of the oxide semiconductor, there are indium gallium zinc oxide(IGZO), indium gallium oxide (IGO), indium zinc oxide (IZO), zincstannic oxide (ZnSnO), and zinc oxide (ZnO), for example.

The second insulating film 12 is formed on the semiconductor layer SC.The second insulating film 12 should be formed of an inorganic materialwhich does not easily cause a defect such as a short-circuit even in athin-film state to function as a gate insulating film. Such an inorganicmaterial may be silicon oxide, silicon nitride, or the like; however, itis not limited thereto, and may be an oxide material such as aluminum,hafnium, or yttrium, or a layered film containing such oxide materials.

The gate electrode WG is formed on the second insulating film 12. Thegate electrode WG overlaps the channel region SCC of the semiconductorlayer. The third insulating film 13 (second insulating film) is formedon the gate electrode WG. In the present embodiment, the thirdinsulating film 13 are formed on the semiconductor layer SC and the gateelectrode WG, and covers a side surface of the second insulating film12. The third insulating film 13 covers the second insulating film 12.Contact holes CH2 and CH3 are formed on the third insulating film 13.Contact holes CH2 and CH3 extend in the third direction Z and passthrough the third insulating film 13.

The source electrode 15A is formed on the third insulating film 13 andpasses through contact hole CH2 to contact the semiconductor layer SC.The drain electrode 15B is formed on the third insulating film 13 andpasses through contact hole CH3 to contact the semiconductor layer SC.

The gate electrode WG, source electrode 15A, and drain electrode 15B areformed of a metal such as molybdenum, tungsten, aluminum, titanium, andcopper or of an alloy of such metals.

The fourth insulating film 14 covers the third insulating film 13,source electrode 15A, and drain electrode 15B. A contact hole CH isformed in the fourth insulating film 14. The pixel electrode PE isformed on the fourth insulating film 14 and passes through the contacthole CH to contact the drain electrode 15B.

FIG. 4 is a cross-sectional view which shows the array substrate ARtaken along line IV-IV of FIG. 2.

A contact hole CH1 is formed to pass through the first insulating film11 and the third insulating film 13. The connection electrode EL isformed on the upper surface of the third insulating film 13 to fill incontact hole CH1. Contact hole CH1 is formed to expose the upper surfaceWGa and a side surface Gc of the gate electrode WG, and the connectionelectrode EL contacts the upper surface WGa and the side surface WGc ofthe gate electrode WG in contact hole CH1. As shown in FIG. 1, theconnection electrode EL contacts the upper surface LSa1 of projectionLSa of the light shielding layer LS. That is, the gate electrode WG1 andthe light shielding layer LS are electrically connected by theconnection electrode EL, and the potential of the light shielding layerLS is fixed to be substantially equal to that of the gate electrode WG.In the present embodiment, the connection electrode EL, source electrode15A and, the drain electrode 15B are formed of the same material. Thefourth insulating film 14 covers the connection electrode EL.

Now, a manufacturing process of the array substrate AR will be explainedwith reference to FIGS. 5 to 10. FIGS. 5 to 10 are cross-sectional viewswhich show a manufacturing method of the array substrate AR of thepresent embodiment. In the manufacturing process of each of FIGS. 5 to10, FIGS. 5A, 6A, and 7A are cross-sectional views of the arraysubstrate AR of FIG. 2 taken along line and FIGS. 5B, 6B, and 7B arecross-sectional views of the array substrate AR of FIG. 2 taken alongline IV-IV.

As shown in the FIGS. 5A and 5B, the light shielding layer LS is formedon the insulating substrate 10. The light shielding layer LS is formedthrough, for example, a photolithography and etching process of atungsten silicide film.

FIG. 6 shows that the process proceeds to the formation of an oxidesemiconductor layer CO. The first insulating film 11 is formed on theinsulating substrate 10 to cover the light shielding layer LS. After theformation of the first insulating film 11, thin-film transistor TR1 isformed on the first insulating film 11 as shown in FIG. 6A. To formthin-film transistor TR1, an oxide semiconductor film such as IGZO isfirst formed on the first insulating film 11 through a sputteringmethod, and then, the oxide semiconductor film is patterned in an islandshape to form the oxide semiconductor layer CO.

FIG. 7 shows that the process proceeds to the formation of the gateelectrode WG. To form the second insulating film 12, an insulating filmis formed on the first insulating film 11 and the oxide semiconductorlayer CO. Then, a metal film used for the formation of the gateelectrode WG is formed on the insulating film. The insulating film andthe metal film are formed through a sputtering method or a plasmachemical vapor deposition (CVD) method, for example. Then, theinsulating film and the metal film are patterned in an island shapealtogether such that the insulating film matures into the secondinsulating film 12 and the metal film matures into the gate electrodeWG. Then, the oxide semiconductor layer CO may be treated to have lowerresistance using the second insulating film 12 as a mask. This treatmentis performed through, for example, a reducing gas plasma process such asa hydrogen plasma process with respect to the exposed oxidesemiconductor layer CO. The exposed oxide semiconductor layer CO isreduced by reducing hydrogen plasma and thus has lower resistance. Theoxide semiconductor layer CO in the area covered with the secondinsulating film 12 is not reduced and thus has relatively highresistance. Consequently, the semiconductor layer SC is obtained fromthe oxide semiconductor layer CO. The method for achieving lowresistance is not limited to the above and may be performed through anyoptional method such as reduction by UV light irradiation.

During the above process, patterning of the insulating film and loweringthe resistance of the oxide semiconductor layer CO can be achieved atthe same time. Specifically, the insulating film is patterned byreactive ion etching (RIE) which is a kind of plasma dry etching. Theetching gas used here may be a gas containing reducing fluorine orhydrogen. The etching gas is a gaseous mixture of methane tetrafluoride(CF4) and oxygen, or a gaseous mixture of perfluorocyclobutane (C4F8),hydrogen, and argon. Thus, the oxide semiconductor layer CO is reducedby fluorine plasma or hydrogen plasma during the patterning of theinsulating film and the metal film. The resistance of the oxidesemiconductor layer CO may not be lowered sufficiently by such a gas fordry etching. However, the oxide semiconductor layer CO with suchauxiliary lowered resistance in the dry etching process is useful toreduce the workload of the resistance lowering process performed later.

FIG. 8 shows that the process proceeds to the formation of the thirdinsulating film 13. As shown in the FIGS. 8A and 8B, the gate electrodeWG is formed, and then, the third insulating film 13 is formed on thefirst insulating film 11 through a plasma CVD method to cover the firstinsulating film 11, semiconductor layer SC, and gate electrode WG, andside surfaces of the second insulating film 12.

FIG. 9 shows that the process proceeds to the formation of contact holesCH1, CH2, and CH3 in the third insulating film 13. As in the FIG. 9A,contact holes CH2 and CH3 are formed in the third insulating film 13 toreach the semiconductor layer SC. As in the FIG. 9B, contact hole CH1 isformed in the first insulating film 11 and the third insulating film 13to reach the light shielding layer LS. Contact hole CH1 is etchedone-layer deeper as compared to contact holes CH2 and CH3 to reach thefirst insulating film 11. The semiconductor layer SC is formed of anoxide semiconductor and is basically untouched by etching. Thus, thesemiconductor layer SC can function as a stopper. Therefore, etching ofcontact holes CH2 and CH3 is stopped at the semiconductor layer SC anddoes not go below the semiconductor layer SC. On the other hand, sincecontact hole CH1 does not overlap the semiconductor layer SC, etching ofcontact hole CH1 is not stopped by the semiconductor layer SC and goesto the light shielding layer LS. With this mechanism, contact holes CH1to CH3 are formed at the same time through the same etching process inthe present embodiment. Furthermore, since the gate electrode WG is notetched, the upper surface WGa and side surface WGc are exposed incontact hole CH1.

FIG. 10 shows that the process proceeds to the formation of the sourceelectrode 15A, drain electrode 15B, and connection electrode EL. As inthe FIG. 10A, the source electrode 15A and the drain electrode 15B areformed on the third insulating film 13. As in the FIG. 10B, theconnection electrode EL is formed on the third insulating film 13.

The metal film formed of molybdenum, tungsten, or the like is formed onthe third insulating film 13, and is filled in contact holes CH1, CH2,and CH3. Then, the metal oxide is patterned in an island shape to formthe source electrode 15A, drain electrode 15B, and connection electrodeEL through the same process.

In the present embodiment, the gate electrode WG and the light shieldinglayer LS are electrically connected through the connection electrode ELformed in contact hole CH1. Thereby, the potential of the lightshielding layer LS is fixed to that of the gate electrode and apotential fluctuation of the light shielding layer LS can be suppressed.Furthermore, the light shielding layer LS includes projection LSa whichprojects from the area where the light shielding layer LS and the gateelectrode WG overlap as shown in FIG. 2. Contact hole CH1 is formed onprojection LSa. Thus, the electrical connection of the gate electrode WGand the light shielding layer LS can be achieved within a small area inthe proximity of the overlapping area thereof. The connection electrodeEL can be formed without affecting high definition performance of thedisplay device.

Furthermore, during the manufacture of the array substrate, contact holeCH1 is formed with contact holes CH2 and CH3 through the samemanufacturing process. The connection electrode EL is formed with thesource electrode 15A and drain electrode 15B with the same materialthrough the same process. Therefore, both the connection electrode ELand thin-film transistor TR1 can be formed through the same process andthe electrical connection of the gate electrode WG and the lightshielding layer LS can be achieved in the same process. That is, thereis no need of performing an additional film formation process or anexposure etching process for the connection electrode EL, and couplingof the light shielding layer LS can be suppressed cost-effectively.

Therefore, the present embodiment can present a display device which cansuppress light leakage current and which can suppress the coupling ofthe light shielding layer cost-effectively.

Now, a variation of the present embodiment will be explained.

FIG. 11A is a plan view which shows a thin-film transistor TR2 in theperipheral circuit portion of a display device of a first variation,FIG. 11B is a cross-sectional view which shows a display panel PNL takenalong line XIa-XIa of the FIG. 11A, and FIG. 11C is a cross-sectionalview which shows thin-film transistor TR2 taken along line XIb-XIb ofthe FIG. 11B.

In the first variation, a gate line G is shaped differently from thegate line of the above embodiment. As in the FIG. 11A, the gate line Gbends at the right angle at the position of thin-film transistor TR1 toextend over the semiconductor layer SC. The gate line G extending overthe semiconductor layer SC is a gate electrode WG.

As in the FIGS. 11B and 11C, an array substrate AR of this variation isstructured substantially the same as the array substrate AR except forthe gate line G, and thus, can be formed through the same process aswith the above embodiment.

The display device of the first variation can achieve the sameadvantages as that of the above embodiment.

FIG. 12 is a plan view which shows an array substrate AR of a displaydevice of a second variation. FIG. 13 is a cross-sectional view whichshows the array substrate AR taken along line XIII-XIII of FIG. 12, andFIG. 14 is a cross-sectional view which shows the array substrate ARtaken along line XIV-XIV of FIG. 12. Comparing the second variation asin FIG. 12 to the above embodiment, the second variation has abottom-gate thin-film transistor TR3.

As in FIG. 12, thin-film transistor TR3 is disposed in the proximity ofa crossing point of a gate line G and a source line S, and iselectrically connected to the gate line G and the source line S.Thin-film transistor TR3 includes a semiconductor layer SC, gateelectrode WG1 formed integrally with a gate line G, source electrode(first electrode) 23A formed integrally with the source line S, anddrain electrode (second electrode) 23B. The source electrode 23A iselectrically connected to the semiconductor layer SC. The drainelectrode 23B is formed in an island shape and is electrically connectedto the semiconductor layer SC. The gate electrode WG1 projects from thegate line G in the second direction Y to overlap a layer above thesemiconductor layer SC.

The pixel electrode PE is electrically connected to the drain electrode23B of thin-film transistor TR3 through a contact hole which is notshown.

The light shielding layer LS overlaps the semiconductor layer SC and thegate electrode WG. A projection LSb is formed on the light shieldinglayer LS to project from the area overlapping the gate electrode WG.Projection LSb extends in a second direction Y which is orthogonal tothe longitudinal direction (first direction X) of the semiconductorlayer SC, and extends in an area overlapping the gate line G. Theconnection electrode EL is formed in an island shape and is electricallyconnected to the gate electrode WG and the light shielding layer LSthrough a contact hole CH4 formed in projection LSb. That is, the gateelectrode WG and the light shielding layer LS are electrically connectedto the connection electrode EL. The connection electrode EL contacts theupper surface and side surface of the gate electrode WG and the uppersurface of projection LSb.

As in FIG. 13, the array substrate AR includes an insulating substrate20, light shielding layer LS, light shielding insulating film 21,thin-film transistor TR3, and the like. The light shielding layer LS isformed on an upper surface 20A of the insulating substrate 20. The lightshielding layer LS is covered with the light shielding insulating film21. Thin-film transistor TR3 is formed above the light shielding layerLS and functions as a switching element. Thin-film transistor TR3includes a gate electrode WG1, gate insulating film 22, semiconductorlayer SC, source electrode (first electrode) 23A, and drain electrode(second electrode) 23B.

The gate electrode WG1 is formed on the light shielding film 21. Thegate insulating film 22 is formed on the gate electrode WG1. The gateinsulating film 22 is formed on the light insulating film 21. Thesemiconductor layer SC is formed on the upper surface of the gateinsulating film 22. The semiconductor layer SC includes a source regionSCS, drain region SCD, and channel region SCC. The channel region SCC isdisposed between the source region SCS and the drain region SCD. Thesource region SCS and the drain region SCD are formed to have lowerresistance as compared to the channel region SCC. The light shieldinglayer LS is formed between thin-film transistor TR3 and the insulatingsubstrate 10, and is opposed at least the channel region SCC of thesemiconductor layer SC.

In this variation, the semiconductor layer SC is formed of an oxidesemiconductor. Note that the light shielding insulating film 21 is afirst insulating film, and the gate insulating film 22 is a secondinsulating film.

The source electrode 23A is formed on the gate insulating film 22 and isalso on the semiconductor layer SC. The drain electrode 23B is formed onthe gate insulating film 22 and is also on the semiconductor layer SC.As above, thin-film transistor TR3 is a bottom-gate thin-filmtransistor.

As in FIG. 14, a contact hole CH4 is pierced through the light shieldinginsulating film 21 and the gate insulating film 22. The connectionelectrode EL is formed on the upper surface of the gate insulating film22 toward the inside of contact hole CH4. The upper surface WG1 a andside surface WG1 c of the gate electrode WG1 are exposed in contact holeCH4, and the connection electrode EL contacts the semiconductor layer SCand the upper surface WG1 a and side surface WG1 c of the gate electrodeWG1 inside contact hole CH4. The connection electrode EL contacts theupper surface LSb1 of projection LSb of the light shielding layer LS asin FIG. 12. That is, in the second variation, the gate electrode WG1 andthe light shielding layer LS are electrically connected by theconnection electrode EL, and the potential of the light shielding layerLS is fixed to be substantially equal to that of the gate electrode WG.The connection electrode EL, source electrode 23A, and drain electrode23B are formed of the same material.

Now, a manufacturing process of the array substrate AR will be explainedwith reference to FIGS. 15 to 19. FIGS. 15 to 19 are cross-sectionalviews which show a manufacturing method of the array substrate AR ofthis variation. In the manufacturing process of each of FIGS. 15 to 19,FIGS. 15A, 16A, 17A, 18A and 19A are a cross-sectional views of thearray substrate AR of FIG. 12 taken along line XIII-XIII, and FIGS. 15B,16B, 17B, 18B and 19B is a cross-sectional view of the array substrateAR of FIG. 12 taken along line XIV-XIV. The formation of each member isperformed in a similar manner to that of the above embodiment, andhereinafter only the parts unique to the bottom-gate thin-filmtransistor will be explained.

As in the FIGS. 15A and 15B, a light shielding layer LS is formed on aninsulating substrate 20.

FIG. 16 shows that the process proceeds to the formation of the gateelectrode WG1. The light shielding insulating film 21 covers the lightshielding layer LS and is formed on the insulating substrate 20. Afterthe formation of the light shielding insulating film 21, a metal filmfor gate electrode WG is formed on the light shielding insulating film21 as in the FIGS. 16A and 16B. The metal film is patterned to form thegate electrode WG.

FIG. 17 shows that the process proceeds to the formation of the gateinsulating film 22. As in the FIGS. 17A and 17B, the gate insulatingfilm 22 are formed to cover the date electrode WG1 and the lightshielding insulating film 21.

FIG. 18 shows that the process proceeds to the formation of the oxidesemiconductor layer CO. A contact hole CH4 in the FIG. 18B is formedthrough the same process as in the above embodiment as shown in FIG. 8.In this variation, the gate electrode WG is not etched, and the uppersurface WG1 a and side surface WG1 c of the gate electrode WG1 areexposed in contact hole CH4. Then, the oxide semiconductor layer CO isformed on the gate insulating film 22 as in the FIG. 18A.

FIG. 19 shows that the process proceeds to the formation of the sourceelectrode 23A, drain electrode 23B, and connection electrode EL. As inthe FIG. 19A, the source electrode 23A and the drain electrode 23B areformed on the gate insulating film 22. As in the FIG. 19B, theconnection electrode EL is formed on the gate insulating film 22.

As in the FIGS. 19A and 19B, a metal film is formed on the gateinsulating film 22 and the oxide semiconductor layer CO and insidecontact hole CH4. The metal film is patterned into an island shape, andthe source electrode 23A, drain electrode 23B, and connection electrodeEL are formed through the same process. In the FIG. 19A, the metal filmis patterned to be divided in an area opposed to the gate electrode WG1to form the source electrode 23A and the drain electrode 23B. The partof the oxide semiconductor layer CO which is not covered with the sourceelectrode 23A or the drain electrode 23B is subjected to an oxidationreduction process and the semiconductor layer SC is formed.

In the display device of the second variation, the gate electrode WG andthe light shielding layer LS are electrically connected through theconnection electrode EL formed inside contact hole CH4. Thereby, thepotential of the light shielding layer LS is fixed to that of the gateelectrode and a potential fluctuation of the light shielding layer LScan be suppressed. Furthermore, the light shielding layer LS includesprojection LSb which projects from the area where the light shieldinglayer LS and the gate electrode WG overlap. Contact hole CH4 is formedon projection LSb. Thus, the electrical connection of the gate electrodeWG and the light shielding layer LS can be achieved within a small areain the proximity of the overlapping area thereof. The connectionelectrode EL can be formed without affecting high definition performanceof the display device.

FIG. 20A is a plan view which shows a thin-film transistor TR4 of adisplay device of a third variation, FIG. 20B is a cross-sectional viewwhich shows a display panel PNL taken along line XXa-XXa of the FIG.11A, and FIG. 20C is a cross-sectional view which shows the displaypanel taken along line XXb-XXb of the FIG. 11A.

In the third variation, a gate electrode WG1 is shaped differently fromthat of thin-film transistor TR3 of the second variation. As in the FIG.20A, the gate line G extends substantially vertically from the gateelectrode WG1 in the third variation. As in the FIGS. 20B and 20C, theother structures of the array substrate AR are the same as that of thearray substrate AR of the second variation, and the array substrate ARis formed through the same process as that of the second variation.

The display device of the third variation can achieve the sameadvantages as that of the above second variation.

As can be understood from the above, the present embodiment and itsvariations can present a display device which can suppress light leakagecurrent and which can suppress the coupling of the light shielding layercost-effectively.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A semiconductor device comprising: an insulatingsubstrate; a semiconductor layer above the insulating substrate; a firstelectrode layer and a second electrode layer which are electricallyconnected to the semiconductor layer; a first metal layer opposed to afirst surface of the semiconductor layer; a first insulating layerbetween the first metal layer and the semiconductor layer; a secondmetal layer opposed to a second surface of the semiconductor layer; asecond insulating layer between the second metal layer and thesemiconductor layer; a third metal layer electrically connecting thefirst metal layer and the second metal layer via one contact holepenetrating the first insulating film and the second insulating film,wherein the first electrode layer, the second electrode layer, and thethird metal layer are all formed of the same material, and the thirdmetal layer directly contacts a top surface and a side surface of thesecond metal layer and a top surface of the first metal layer.
 2. Thesemiconductor device of claim 1, wherein the semiconductor layer isformed of an oxide semiconductor.
 3. The semiconductor device of claim1, wherein the first metal layer or the second metal layer includes agate electrode.
 4. The semiconductor device of claim 1, wherein thefirst insulating layer or the second insulating layer includes a gateinsulating film.
 5. The semiconductor device of claim 1, wherein thefirst electrode layer and the second electrode layer contact a topsurface of the semiconductor layer which is the first surface or thesecond surface.